Abstract:

Impulsivity is associated with addiction in many human studies. Delay discounting (DD) is often used to measure impulsive choice in humans and animals. In DD testing, a small immediate reward is pitted against a larger delayed reward, and relative preference is assessed. The relative contribution of ethanol to impulsivity in alcoholism is not well-understood, therefore I will test the hypothesis that ethanol exposure will increase impulsivity in High Alcohol Preferring (HAP) mice as measured in an adjusting amount DD task.
Selectively bred HAP mice were exposed to ethanol and tested in DD in 3 different experiments. Experiment 1: ad lib homecage ethanol drinking for 21 days and 17 days were used to expose mice to ethanol. Additionally, mice were tested in DD while “currently drinking” vs. “abstinent”. In experiment 2, to achieve higher blood alcohol concentrations, mice were injected with 3.5 g/kg ethanol 8 times and tested before and after in DD. In both experiments 1 and 2, mice were tested at only 2 delays (0.5 sec and 10 sec), to maximize sensitivity to detect shifts in choice behavior. In experiment 3, mice responded for 8% ethanol or 0.01% saccharin at a full range of delays: 0, 1, 2, 4, and 8 sec.
Experiment 1 did not reveal any impact of ethanol drinking on impulsivity. Experiment 2 revealed a strong trend of reduced impulsivity in the 10 sec delay group after ethanol injections. Experiment 3 revealed reduced impulsivity at the 8 sec delay in the group responding for ethanol, and also revealed a significant correlation between higher ethanol drinking and reduced impulsivity.
These data were unexpected, and imply that the a priori hypothesis not only should be rejected, but that the opposite hypothesis may be true: ethanol decreases impulsivity, at least with high dose exposure and in responding for it as a reinforcer. This effect was similar to the effect observed in other studies with amphetamine, which consistently decreases impulsivity. Ethanol may have been exerting an amphetamine-like effect on impulsivity at the doses tested here. There is no evidence in the data generated in these studies that ethanol increases impulsivity.